This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ PrePrints) and either DOI or URL of the article must be cited.

Abstract

The accelerated increase of nitrogen deposition is the third cause of biodiversity loss, as a result of saturation of ecosystems worldwide. The effects of nitrogen deposition on the endemic and endangered neotropical epiphytic orchid, Laelia speciosa, were evaluated via a dose-response experiment and a stable isotopic field assessment for individuals from a city and from an oak forest, in order to evaluate the potential risk facing this orchid, and record the history of the nitrogen deposition of series of consecutive annually produced pseudobulbs. Lower doses of nitrogen of up to 20 kg N ha yr–1 the dose that led to optimal performance of plants, acted as fertilizer. For instance, chlorophyll content and chlorophyll fluorescence (Fv/Fm) peaked at 0.66 ± 0.03 g m-2 and 0.85 ± 0.01, respectively. In contrast, toxic effects were observed at the higher doses of 40 and 80 kg N ha yr–1, leading a decrease of 38% of the chlorophyll content and 23% of the chlorophyll fluorescence. For the field assessment, a tissue nitrogen content of 1.2 ± 0.1% (dry mass basis) for the orchids suggested non-toxic deposition rates both at the city and the oak forest. However, their respective isotopic signatures revealed different sources of N at each site. Indeed, in the oak forest δ15N amounted –3.1 ± 0.3‰, typical of places with low industrial activities, while in the city the δ15N reached 5.6 ± 0.2‰, typical of sites with some degree of industrial and automobile activity. Laelia speciosa would be an adequate bioindicator of nitrogen deposition because its ability to take up nitrogen from the atmosphere while preserving its isotopic signature and showing aclear physiological response to increasing inputs of nitrogen. However, its limited geographical distribution precludes the orchid as an ideal candidate for biomonitoring. Thus other vascular epiphytes should be considered for this purpose.

Author Comment

This manuscript will be submitted to PeerJ for review and it is part of the doctoral dissertation of EA Díaz-Álvarez.

Additional Information

Competing Interests

The authors declare they have no competing interests.

Author Contributions

Edison A. Díaz-Álvarez conceived and designed the experiments, performed the experiments, analyzed the data, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.

Roberto Lindig-Cisneros conceived and designed the experiments, contributed reagents/materials/analysis tools, reviewed drafts of the paper, closely supervised the plant nutrition portion of the experiments.

Casandra Reyes-García conceived and designed the experiments, contributed reagents/materials/analysis tools, reviewed drafts of the paper, adviced and supervised on the stable isotopes portion of the study.

Erick de la Barrera conceived and designed the experiments, contributed reagents/materials/analysis tools, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.

Field Study Permissions

The following information was supplied relating to field study approvals (i.e., approving body and any reference numbers):

Funding

This work was funded by the Dirección General del Personal Académico, UNAM an institutional funds of Centro de Investigaciones en Ecosistemas, UNAM. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Add your feedback

Before adding feedback, consider if it can be asked as a question instead, and if so then use the Question tab. Pointing out typos is fine, but authors are encouraged to accept only substantially helpful feedback.

Follow this preprint for updates

"Following" is like subscribing to any updates related to a preprint.
These updates will appear in your home dashboard each time you visit PeerJ.

You can also choose to receive updates via daily or weekly email digests.
If you are following multiple preprints then we will send you
no more than one email per day or week based on your preferences.

Note: You are now also subscribed to the subject areas of this preprint
and will receive updates in the daily or weekly email digests if turned on.
You can add specific subject areas through your profile settings.